Mechanism for cutting lower thread in a sewing machine



y 9, 1968 TADASI KOZUKA 3,391,665

MECHANISM FOR CUTTING LOWER THREAD IN A SEWING MACHINE Filed June 16. 1967 5 Sheets-Sheet 1 I g I 774M K INVENT UR Jul y 9,1968

TADASI KOZUKA MECHANISM FOR CUTTING LOWER THREAD IN A SEWING MACHINE Filed J1me 16, 1967 3 Sheets-Sheet 2 W k INVEBITOR.

' Jilly 9. 1968 I TADASI KOZUKA 3,391,

MECHNISM FOR CUTTING LOWER THREAD IN A SEWING MACHINE Filed June 16.1967 v s Sheets-Sheet 3 LL F ll 1 7 Fig. 6

11-55- 4 L JJZ United States Patent 3,391,665 MECHANISM FOR CUTTING LOWER THREAD IN A SEWING MACHINE Tadasi Kozuka, Tokyo, Japan, assignor to Tokyo Juki Kog o Kabushiki Kaisha, Tokyo, Japan Filed June 16, 1967, Ser. No. 646,650 1 Claim. (Cl. 112-252) ABSTRACT OF THE DISCLOSURE Mechanism for cutting the lower thread in a sewing machine comprising a lever rotatably fixed to said sewing machine, an arm provided adjacent to the needle plate base and operably coupled with said lever, a thread pulling member fixedly attached to said arm and a thread cutting device including a stationary cutting blade and a movable cutting blade driven by said lever through said arm, said arm being located on the lower surface of the needle plate base on the bed of said sewing machine, said thread pulling member being adapted to move across the lower surface of the needle hole in the needle plate base thereby pulling out the lower thread from the bobbin to provide sufiicient length of the thread for successive operations, said arm being moved further so that said cutting device is operated between the upper surface of said needle plate base and the needle plate located on the upper surface of said needle plate base so as to shear off the thread after the thread is pulled out of the bobbin sufiiciently by said thread pulling member.

Background of the invention The present invention relates to a sewing machine and particularly to a mechanism for cutting the lower thread in a sewing machine.

In a conventional sewing machine heretofore used, the end portion of the lower thread extending from the bobbin which is housed in the bobbin case is made freewhen the first stitch is to be made on the cloth to be stitched; therefore, if the length of the lower thread extending from the bobbin is too short, the upper thread held by the needle which is raised by the first operation of the thread take-up lever will not intersect the lower thread when the thread comes off the under looper, so the stitch cannot be formed. On the other hand, if the length of the lower thread is too long, the free end of the lower thread extends too far under the lower surface of the cloth with the result that an unattractive stitch is formed in the cloth. And further, in the mechanism for cutting the lower thread in the prior art, the thread cutting blades are rotatably mounted on the lower surface of the needle plate; therefore, the prior art mechanism has many disadvantages. For example, it is necessary to take the cloth feeding plate and needle plate base off from the upper surface of the bed in order to change the cutting blades, thus making the operation very troublesome.

Summary of the invention The present invention avoids the above-mentioned disadvantages by providing the cutting blades and thread pulling member on the upper surface and lower surface of the needle plate base, respectively, and by allowing one of the cutting blade-s and the thread pulling member to be rotated adjacent to the needle point.

Therefore, an object of the present invention is to provide a novel and useful mechanism for cutting the lower thread in a sewing machine which avoids the disadvantages inherent in the prior art.

Another object of the present invention is to provide a novel and useful mechanism for cutting the lower thread in a sewing machine wherein the cutter blades and thread pulling member are rotatably mounted adjacent to the needle hole on the upper surface and lower surface of the needle plate base, respectively, so that changing of the cutting blades can be etficiently and conveniently made.

A further object of the present invention is to provide a novel and useful mechanism for cutting the lower thread in a sewing machine which can perform correct stitching operation at the beginning of the operation, and which can provide good looking stitches in the cloth by providing an appropriate length of the lower thread extending from the bobbin after cutting operation is effected.

These and other objects and advantages of the present invention will be clearly understood by reading the following description of an embodiment of the present invention in connection with the accompanying drawings illustrating the embodiment.

Brief description of the drawings FIG. 1 is a side view of the main parts of an embodiment of the present invention,

FIG. 2 is a di-agrammatical view seen in the direction of arrow II, II in FIG. 1,

FIGS. 3 and 4 are a plan and rear side views of the needle plate base of the present invention, respectively,

FIG. 5 is a diagrammatical view seen in the direction shown by the arrow V, V in FIG. 1, and

FIG. 6 is a cross-sectional view taken along the line VIVI in FIG. 3.

Description of the preferred embodiment Now referring to the drawings, the preferred embodimerit of the present invention will be described in detail. As shown in FIGS. 1 and 5, a lever 4 is pivotally secured to the side of vertical standard 3 by bolt 5 so as to extend to the rear side of the sewing machine (the side opposite to the operator), said vertical standard 3 being secured to bed 1 of the sewing machine which is adapted, for example, to cross-stitch buttons and the like. Overhanging arm 2 is integral with said vertical standard 3. One end of spring 6 is fixed to lever 4 inter-mediate the length thereof by a thread fixed to lever 4, and the other end of spring 6 is fixed to the rear side of over-hanging arm 2 so as to urge said lever 4 clockwise. Said lever 4 is drivable in the anticlockwise direction by operating a pedal (not shown) through a chain (not shown) which is connected between the outer end of lever 4 and the pedal. A driving arm 9 is pivotally secured to the side of vertical standard 3 by bolt 10, the lower end of said driving arm 9 loosely passing through hole 8 of bed. 1 into the interior thereof. A round headed pin 7 is provided at the lower end of said driving arm 9. Lever 4 and driving arm 9 are coupled with each other by means of link 11 which is rotatably secured at each end to lever 4 and driving arm 9, respectively. As shown in FIGS. 3 and 6, needle hole 13 is provided in needle plate base 12 substantially at the center thereof, said needle plate base 12 being mounted on bed 1. Needle plate 16 is fixedly secured to the upper surface of said needle plate base 12, said needle plate 16 being provided with a hole 14 in alignment with said needle hole 13 of needle plate base 12 and a recess 15 formed in the lower surface of needle plate 16 so that said hole 14 is located within the area of said recess 15. Said recess 15 provides a space between needle plate base 12 and needle plate 16 around needle hole 13. A stationary cutting member 17 is fixedly secured to the upper surface needle plate base 12 adjacent to said needle plate 16 at the side toward the operator by means of screw threads 18 fixed to needle plate base 12, so that cutting blade 19 which is formed at the tip of said cutting member 17 by bending the tip portion thereof upwardly projects into said recess so as to be positioned in opposing relationship to said needle hole 13. Movable cutting member 23 is rotatably secured to the upper surface of needle plate base 12 by means of screw thread 24 fixed to said needle plate base 12 at the rear side of said needle plate 16 (opposite to the side at which stationary cutting member 17 is located). Said movable cutting member 23 is provided with cutting blade 20 formed at the transversely bent tip end thereof and a pin 22 projecting downwardly therefrom through elongated hole 21 in needle plate base 12. As shown in FIG. 3, when movable cutting member 23 is rotated clockwise so that cutting blade 21 thereof moves across the upper end of needle hole 13 and reaches stationary cutting blade 19, the lower thread which extends downwardly from hole 14 and leads to the bobbin (not shown) through needle hole 13 is sheared off by the cooperation of cutting blade 19 of stationary cutting member 17 and cutting blade 20 of movable cutting member 23. As shown in FIGS. 4 and 6, guide member 26 having guide surface 25 formed by bending the guide member 26 downwardly at its intermediate portion is fixedly secured to the lower surface of said needle plate base 12 adjacent to the left end thereof, while an arm 28 is rotatably secured at 29 on the lower surface of needle plate base 12 at the right hand end thereof, said arm being provided with a guide hole 27 which engages with pin 22 of movable cutting member 23 projecting downwardly therefrom through hole 21 of said needle plate has 12. Thread pulling member 30 is fixedly secured to the lower surface of arm 28, the intermediate portion of said thread pulling member 3t? being bent upwardly so as to form thread pulling portion 31 which is located adjacent to the lower surface of needle plate base 12, said thread pulling portion 31 being shaped such that is does not interfere with the needle (not shown) when the needle is moved downwardly through needle hole 13. The tip portion of said thread pulling member 39 is bent downwardly so as to contact with the upper guide surface 25 of guide member 26 (FIG. 6) so that said guide member is prevented from moving downwardly. As shown in FIGS. 1 and 2, the bifurcation 34 at the right hand end of guide rod 33 which is pivotally secured by screw thread 32 to the lower surface of bed 1 is engaged with pin 7 projecting from the lower end of driving arm 9, the left hand end of said guide rod 33 being rotatably connected to one end of rod 35 the other end of which is rotatably connected to arm 28 as shown in FIG. 4. Cloth feeding plate 37 is shiftably provided on the upper surface of said needle plate base 12 with the elongated hole 36 of said feeding plate 37 being slidably fitted with needle plate 16, said cloth feeding plate 37 being driven by the driving motor of the sewing machine (not shown) so as to feed the cloth to be stitched in desired direction.

As shown in FIG. 2, the relative positions of guide hole 27 of arm 28, hole 21 of needle plate base 12 and pin 22 of thread cutting member 23 at the resting position of the sewing machine are such that pin 22 engages with the front end of hole 27 (the end which faces to the operator) and with the rear end of hole 21. When arm 28 is rotated anticlockwise as seen in FIG. 2 (i.e. clockwise as seen in FIG. 4), the rear end of guide hole 27 first abuts against pin 22 while it is in rest position by the rotation of arm 28 thereby pulling out the lower thread sufliciently by the movement of pulling member 30 secured to arm 28 across needle hole 13 in the forward direction, i.e. toward the operator. Further movement of arm 28 causes pin 22 to be moved in hole 21 of needle plate base 12 by the engagement of the rear end of hole 27 with pin 22 until pin 22 abuts against the forward end of hole 21 (i.e. the end which faces to the operator) thereby causing thread cutting member 23 to be rotated clockwise about the axis of thread 24 so that cutting blade 20 of cutting member 23 moves across needle hole 13 in the forward direction (toward the operator) to cooperate with stationary cutting member 17 thereby shearing off the thread.

Since the present invention is constructed as stated above, each part of the thread cutting mechanism is in the position as indicated by solid line in FIGS. 3, 4 and 5 when the sewing machine is operated. When the machine is stopped and the pedal is operated to rotate lever 4 anticlockwise against the action of spring 6 as shown in FIG. 5, each part of the mechanism is thereby moved to the position as indicated by double dot chain line in FIGS. 3, 4 and 5, lever 4 being rotated anticlockwise together with the end of link 11 rotatably fixed to said lever 4 as shown in FIG. 5, link 11 causing driving arm 9 to be rotated clockwise by the connection of link 11 with driving arm 9, thereby rotating guide rod 33 anticlockwise by the engagement of bifurcation 34 thereof with pin 7 at the lower end of driving arm 9 as shown in FIG. 2. Thus, arm 28 is rotated anticlockwise as shown in FIG. 2 (clockwise in FIG. 4) through rod 35 the respective ends of which are rotatably fixed to the left hand end of guide rod 33 and arm 28 until pin 22 abuts against the rear end of hole 27 in arm 28. Thread pulling member 30 fixed to arm 28 is thus rotated in the same direction as that of rotation of arm 28 with the tip portion of thread pulling member 30 contacting with the upper surface of guide surface 25 of guide member 26, and, at the same time, thread pulling portion 31 of thread pulling member 30 moves across the lower surface of needle hole 13 upwardly as seen in FIG. 4 (downwardly as seen in FIG. 2) thereby pulling out of the lower thread which is fed from the bobbin. Arm 28 further rotates until pin 22 which engages with the rear end of hole 27 (FIG. 2) abuts against the forward end of hole 21 of needle plate base 12 thereby rotating movable thread cutting member 23 mounting pin 22 thereon clockwise as seen in FIGS. 1 and 3 so that cutting edge 20 of movable thread cutting member 23 cooperates with cutting edge 19 of stationary cutting member 17 to shear off the lower thread. When lever 4 is released from the lower position by releasing the pedal, each part of the mechanism returns to the position shown by solid line in FIGS. 4, 5 and 6.

Since the present invention thus far described provides lever means rotatably fixed to the sewing machine by the operation of the pedal, which lever rotates the arm rotatably fixed to the lower side of the needle plate base on the bed of the sewing machine through various elements coupled to said lever thereby causing the thread pulling member to move across the lower surface of the needle hole of the needle plate base thereby pulling the thread coming from the bobbin to provide sufficient length of the thread for successive operation of the sewing machine, thereafter the thread cutting member being caused to move into the recess provided in the lower surface of the needle plate across the thread hole to shear off the thread after the thread is pulled by the thread pulling member to provide sufficient length thereof for successive stitching operation, the cutting operation of the lower thread can be effected very easily and quickly by merely operating the pedal, while the thread is pulled out sufiiciently form the bobbin before the cutting of the lower thread is elfected so that the sewing machine is ready for the next operation, and, at the same time, the appearance of the stitching is excellent because the length of the lower thread extended from the stitch in the cloth at the beginning of the stitching operation is controlled. The present invention also insures that stitches will be formed at the beginning of the stitching ope-ration, because the sutficient length of the lower thread provided by the cutting device of the present invention after it is sheared off will be twined with-out fail with the loop of the upper thread. Further, since the thread is sheared off in the recess provided in the lower surface of the needle plate located on the upper surface of the needle plate base, no excess length of the thread is left after it is cut off as is the case in the prior art wherein the thread is cut at a position below the needle plate base thereby insuring that good looking stitches will be formed on the cloth. Further, the cutting edges can be changed very easily and quickly by merely removing the cloth feeding plate shifta'bly positioned on the upper surface of the needle plate base.

I claim:

1. Mechanism for cutting the lower thread in a sewing machine comprising a lever rotatably fixed to a needle plate base having a needle hole and a needle plate mounted on the upper surface of said base, a bobbin holding said lower thread, an arm to the needle plate base and operatively coupled with said lever, a thread pulling member fixedly attached to said arm and a thread cutting device including a stationary cutting blade and a movable cutting blade driven by said lever through said arm for cutting the thread in cooperation with said stationary cutting blade, the improvement comprising said arm being located on the lower surface of the needle plate base, said thread pulling member being adapted to move across the lower end of the needle hole in the needle plate base by the movement of said arm thereby pulling out the lower thread from the bobbin to provide a sufficient length of thread for successive operations of the sewing machine, said arm being adapted to be moved so that said cutting device is operated between the upper surface of said needle plate base and the needle plate so as to shear off the thread after the thread is pulled out sufiiciently from the bobbin by the operation of said thread pulling member, said thread pulling member and said thread cutting device being returned to their initial positions by the return movement of said lever.

References Cited UNITED STATES PATENTS 1,234,258 7/ 1917 Barron 112--252 1,373,227 3/1921 Fifield 112-252 1,841,102 1/1932 Fifield 112-252 2,376,417 5/1945 Chudner 112-252 3,234,900 2/1966 Harris 112--252 HERBERT F. ROSS, Primary Examiner. 

